DESCRIPTION: (Adapted from the abstract.) The long range goal of the proposed research is to understand the role of PAX3-FKHR in alveolar rhabdomyosarcoma (ARMS), a tumor of fetal skeletal origin that is most common in children. PAX3-FKHR is a product of t(2;13) ARMS-associated chromosomal translocations. This chimeric transcription factor contains the PAX3 DNA binding domain and the (stronger) FKHR transactivation domain. Preliminary studies show that PAX3-FKHR aberantly activates the gene for the platelet derived growth factor alpha receptor (PDGFaR). This is the first example of a cellular target gene that is specifically affected by PAX3-FKHR and not PAX3. The first specific aim is to delineate the PAX3-FKHR response element that flanks the PDGFaR gene. The second aim is to map the protein motif(s) in PAX3-FKHR that enables it to activate the PDGFaR gene. The third aim is to examine how PDGFaR function contributes to ARMS tumor cell growth. Since PDGF is a potent mitotic growth factor, aberrant expression of its receptor is likely to play a crucial role in cell transformation.